Digital pixelated non-emissive displays require conductive tracks running to the electrodes at every pixel to address the display. The display can be transparent and lit from behind or rely on a reflector on one side, using ambient light to view the device. In the case of displays which are illuminated from behind, the tracks carrying the current must be substantially transparent over the viewing area. They may be made of an organic conductor such as polythiophene, a derivative of polythiophene, which may be mixed with other components or an inorganic conductor such as indium tin oxide (ITO). The track and electrode pattern may be formed in any suitable manner such as photolithography and then etched with a suitable etchant. However, these ‘conductive’ materials have a relatively large resistance when used to form transparent conductors and this resistance will impair the operation of a display, especially if the display is large.
A means of overcoming this is to put a conducting metal over part of these tracks to reduce the resistance. This reduces the light passing through the pixels. The area covered by the metal is kept to a minimum. If the display is backlit, the effect of the metal conductors can be partially overcome by making them reflective. Any light hitting the metal conductor would then be reflected back into the light box or light guide instead of being absorbed.
In the case of a light box, it is necessary that the metal conductor be highly reflective but not necessarily highly specular. However, to reduce the thickness of the display, especially, for example, in portable high resolution displays, it is common practice to use edge lighting of a planar wave guide structure which is designed to leak some of the light from one side of the light-guide and uniformly illuminate the display. In this case it is important that the reflection from the metal conductor be specular to avoid breaking the wave guiding conditions and causing light leakage which would reduce both the efficiency and the uniformity of the backlight. Therefore, a reflective metal conductor with a good mirror finish on the ITO substrate would be advantageous in both cases. This metal is often coated by vacuum deposition or sputtering and then subsequently laser etched. This process is slow and requires the formation of a good vacuum around the material. This puts a limit on the practical size of rigid transparent substrates such as glass or requires a rolled up flexible substrate to be rolled and unrolled within the vacuum.
U.S. Pat. No. 6,774,965 discloses a combination of metal and transparent conductors. This document teaches the use of ITO as the transmissive electrode and the use of a top metallic reflective conductor to reflect light from the surroundings to give a transflective display. U.S. Pat. No. 6,774,965 does not teach the use of the metallic conductor to reflect light back into the light box behind the display and indeed creates structure behind the reflecting electrodes that absorb light. The method of manufacture is consecutive and new resist steps, dry or wet are implied at each stage.